1. Field of the Invention
The present invention relates generally to a method for controlling an electrically power-assisted steering apparatus for vehicles; and more particularly, an apparatus for controlling an electrically power-assisted steering device for vehicles including a filter.
2. Description of Related Art
Electrically power-assisted steering devices, also referred to as an EPAS (Electric Power Assisted Steering) system, provide a power steering force. With an EPAS system an electric motor either applies a rotational force to a steering shaft connected to a steering pinion of a rack-and-pinion steering gear mechanism or applies a linear force to the steering rack. In such systems, the electric motor is usually controlled at least as a function of an input torque applied to a steering wheel by a driver of the vehicle, and a vehicle speed which is determined.
Two methods of applying rotational force are known, one determines the power steering force to be applied by the electric motor using a static boosting curve, also referred to as a static boost curve. The static boosting curve defines a static relationship between the input torque applied by the driver and the power steering force or assisting torque generated by the electric motor. The boosting curve can be a function that can be calculated or a characteristic curve diagram that is stored in advance, the function and diagram both include the driver input torque and vehicle speed as input variables. An advantage of using a static boosting curve is the ease of adjustment of the boosting curve. However, a disadvantage is that it does not take into account the dynamic behavior of the steering device since the control itself is static and cannot act dynamically.
Another method for uses a boosting curve including a dynamically regulated EPAS system. The electrically power-assisted steering device is regulated using an active, dynamic control unit, for example by means of a PID control unit, wherein the control unit is setpoint-value-controlled and the control device usually includes a setpoint signal value transmitter.
An active, dynamic control of a power steering force is known, for example, from EP1431160B1 that describes an electrically power-assisted steering device of a vehicle to which a power steering force or a steering assistance torque is applied by means of a motor. In particular, a system for controlling the steering properties experienced by the driver and the absolute value of the adverse effects from the road transmitted to the driver, in which the steering properties are determined and controlled independently of the control of the transmission of the adverse effects of the road. The system includes a setpoint signal value transmitter for calculating a setpoint steering wheel torque which is to be felt by the driver of the vehicle, as well as a first control unit and a second control unit which acts in parallel with the first control unit. The first control unit controls, through cooperation with the second control unit, a motor control unit which in turn controls the motor. The second control unit damps undesired adverse effects from the road, with the result that said adverse effects are not transmitted to the driver.
Although the dynamic control has significant advantages over the static control by means of a boosting curve, the currently known dynamically controlled EPAS systems are also defined by relatively poor feedback about the primary driving state of the vehicle, for example steering torques, resulting from the caster of the steered vehicle wheels or the transverse acceleration of the vehicle, to the driver by means of the steering device since the information which is transmitted to the steering device by the vehicle chassis is generally interpreted as being noise by the control device and/or compensated. This causes the steering sensation of active, dynamically controlled EPAS systems to be frequently perceived by drivers as being synthetic.
An improvement in this regard is performed by a dynamic control of an electrically power-assisted steering device of a vehicle which is disclosed in EP 2 397 390 A1. As set forth therein, a setpoint signal value transmitter feeds a setpoint value to a control unit of the steering device including a forward model or structural mapping of the steering device with a plurality of individual elements such that the structural mapping can be described by means of easily comprehensible parameters such as, for example, friction, rigidity, damping or absolute value of the feedback of road properties, and in this way the behavior of the real steering device can be adapted to the behavior of the structural mapping.
The present invention has as one object specifying a method for controlling an electrically power-assisted steering device for vehicles, in particular motor vehicles, and a device for controlling an electrically power-assisted steering device for vehicles, with the method and device providing a driver with an improved steering sensation which is, in particular, more realistic in terms of the feedback about the primary driving state of the vehicle. The primary driving state of the vehicle is to be understood as being, in particular, the information transmitted by the chassis of the vehicle to the steering device, for example the driving properties of the vehicle which result from the caster of the steered vehicle wheels or the transverse acceleration of the vehicle and which are intended to communicate the desired driving or steering sensation to the driver. In addition, this object is to be achieved in the simplest way possible.